Takman, Maria

Abstract [en]

The drinking water production in Sweden is facing challenges because of climatic changes, eutrophication and brownification, which contributes to an increase of algal blooms. This can lead to a production of different types of toxins, and the most common group of algal toxins is the hepatotoxic microcystins (MC). Other algal toxins that occur in Sweden are anatoxin-A (ATX-A) and the paralytic shellfish toxins (PST), which are neurotoxic. Flocculation and filtration has been shown to reduce intracellular MC, but to reduce extracellular MC it seems like other techniques are needed, such as membrane filtration, active carbon or ozone. It has also been shown that dissolved organic carbon (DOC) might affect the reduction of MC, either through occupying adsorption spots on the membrane, or through bindings between MC and DOC.

In this project, the reduction of four types of added MC (microcystin-LR, microcystin-RR, microcystin-LY and (D-Asp3)microcystin-LR) with two nanofilters (NF) (with molecular weight cutoff (MWCO) 300-500 Da and 1000 Da) and one ultrafilter (UF) (MWCO 10000 Da) was studied. Further, the sorption between toxins and membrane or between toxins and DOC was studied. Water samples from three Swedish lakes were used to achieve a varying DOC-character. The reduction was also studied in synthetic water (MilliQ-water with adjusted pH and conductivity). This was done in order to study if the reduction was affected of the presence of DOC. The reduction of ATX-A and PST was studied in one experiment, with an NF-membrane (MWCO 1000 Da). The studied PST’s were saxitoxin (STX), N-sulfocarbamoyl-gonyautoxin-2 (C1) and Gonyuatoxin‑2 (GTX2).

MC was reduced to under the limit of detection for all NF-experiments, while a low or no reduction was observed with UF. MC-RR was the toxin that, to the biggest extent, bound to the membrane or to DOC. MC seemed to bind to the membrane or to DOC to a higher extent when the DOC was hydrophilic and low molecular autochthonous, as compared to when the DOC was allochthonous. The reduction of ATX-A and PST was 20 – 40 %, with a reduction that declined during the experiment. C1, the PST with highest molecular weight and lowest net charge, was reduced to the lowest extent, while STX, the PST with the lowest molecular weight and the greatest net charge, was reduced to the highest extent. This implies that size exclusion was not a contributing reduction mechanism for ATX-A or PST, while electrostatic mechanisms probably were more important.